


Byleth, the broken Ashen Demon

by MidnightJoker



Category: Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Byleth is a dragon, Dragon au!, Dragon! Byleth, F/M, Female My Unit | Byleth, My Unit | Byleth Has Emotions, Said dragon can end the world
Language: English
Status: In-Progress
Published: 2021-03-08
Updated: 2021-03-11
Packaged: 2021-03-14 20:54:44
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 4
Words: 1,735
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29922699
Author URL: https://archiveofourown.org/users/MidnightJoker/pseuds/MidnightJoker
Summary: Following the death of Jeralt, Byleth and her new dragon form uses her powers to revive him and slaughter anyone who stands in her way.
Relationships: Dimitri Alexandre Blaiddyd/My Unit | Byleth
Kudos: 10





	1. The discovery.

**Author's Note:**

> Headcanons:  
> In dragon form, Byleth has her own divine pulses and uses it infinitely.  
> Byleth's dragon form, The Ashen Demon, is capable of destroying the world.  
> Seteth, Flayn, and Jeralt knew about this and try to prevent to much grief for Byleth to prevent her transformation.  
> Rhea and the rest of the monastery knew of Byleth's transformation before anyone else.

**(At the end of the chapel mission. I forgot the name already.)**

"F-Father..." Byleth begins as tears run down her cheeks. "Don't... leave me..."

"Sorry, kid..." Jeralt grunts "Guess your going to have to go your own path..."

Byleth looked upwards, Monica was running away.. But then _it_ has begun...

Her transformation...

She had noticed that her hands had become scaly, wings popped out of her back as horns popped out her head, she grew a tail as the now human Byleth was gone, leaving a dragon-like beast in her place..

"P-Professor?" Dimitri asked. the Blue Lions, and Flayn were shocked.. Byleth had shown her true Ashen Demon form.

"GWAAAAAAAAAAAAOOOOOOOOOOHHHHHHHHHHHHHH!" The dragon roared, all around the blue Lions, they appeared to go back in time, back before Monica stabbed Jeralt.

**(Back before Monica stabs Jeralt)**

"Thank you so much Captain!" Monica chirped. She grabs her dagger and turns around to stab Jeralt, but when she turns around a dragon is standing in front of Jeralt defensively standing in front of him, as a sort of way of protecting him.

"Eh?" Monica wondered as she stared at the dragon.

"GRAWWWWWWWWWWWWWWWWRRRRRRRRRR!" The dragon booms, Monica drops her dagger and begins to run off, but is caught by the Ashen Demon.

"Let me go!" Monica cried as the Ashen Demon lifted her into the air, the dragon ran through the chapel grounds dragging Monica in it's claws. The dragon flew a little higher before descending onto the chapel grounds as Monica's face met the rough rocky road of the chapel.

"RAAAAAAAAAAAAAAAAAAOOOOOOOOOOOHHHHHHHHHHHHHHH!" The dragon roared before slamming the heavily injured Monica into the rock filled road.

"Kid?" Jeralt wondered. "Kid?"

No response...

"Answer me, Kid!" Jeralt exclaimed.

"Grrrroah..." The Ashen Demon growled quietly before fleeing.

"I... No..." Flayn whispered quietly.

"Flayn?" Anette asked. "What's the matter?"

"I've only studied the Ashen Demon once..." Flayn begins. "We must warn my brother and everyone in the monastery!" Mercedes used a spell to warp all of them back to the monastery.

**(Garreg Mach Monastery, Jeralt lives)**

"Brother, Brother!" Flayn yelled as she ran towards Seteth who was headed back to his office.

"What is it?" Seteth asked.

"The professor, she turned into that _ancient beast."_ Flayn sighed. Seteth already stopped.

"She turned into _that_ thing?" Seteth asked.

"This is my daughter we're talking about." Jeralt begins. "I'd appreciate a little more respect when we're talking about my kid."

"We must inform Rhea, at once." Seteth says. the group runs off but bumps into Rhea.

"Lady Rhea." Jeralt begins. "Do you know anything about a black dragon?"

"The Ashen Demon..." Rhea sighed. "Alright, I will tell you.."

"You all know about this?" Dimitri asked.

"Long ago..." Rhea begins. "A dragon/human child was prophesized to be born... If this child was to be born it would cause the end of our world, Jeralt is the only one that can calm it down which explained why it never attacked him."

"But why would it be Byleth?!" Jeralt asked.

"This dragon child would look like it's mother, if to much grief is placed on this child it will turn into a dragon and attempt to destroy humanity.. There are only two things that stop it." Rhea sighed.

"They are?" Dimitri wondered.

"The goddess herself..." Rhea begins. "Along with all the heroes' relics. As long as one or the other makes contact with the beast's flesh, we might stand a chance."

"professor..." Dimitri begins to himself. "We will rescue you.."

**(End of chapter 1)**


	2. Human Ashen Demon in the Holy tomb.

**Summary for the Chapter:**

> Set during the battle in the Holy tomb along with the one at Garreg Mach. The Ashen Demon has control over both forms of Byleth and wishes to take out humanity, one army at a time.

**Notes for the Chapter:**

> (What if there was another child of the goddess, Sothis?  
> This is the Ashen Demon, Lol)

**(Set before the battle of the Holy tomb)**

"That Ashen Demon Dragon thing..." Dimitri begins "It's controlling the professor?"

"I'm afraid so." Flayn sighed. "The longer we take, the smaller the chance our professor will survive the Demon's control."

"You kids don't want to miss the chance at visiting the holy tomb, do you?" Jeralt asked before turning around. "I just wish my kid is fine."

"She will be fine, Jeralt.." Rhea answered. "We must head over there... To pray that our dear professor is free from control." The group of Blue Lions were followed by the knights of Serios and Rhea, they were headed for the Holy Tomb.

_"Hang in there, professor...."_ Dimitri thought. _"We'll save you."_

**(In the Holy Tomb)**

"Huh?" Dimitri wondered. "Someone's already here?" The person started slowly clapping as they turned around, it looked like Byleth... If she had red eyes and hair.

"Oh, hello there..." The person begins. "So nice to see that humans have even bothered to check up on me."

"It's _her._ " Rhea begins. "The Ashen Demon."

"Yeah, Yeah." The Ashen Demon begins as she sighed. "Still trying to revive mother, huh?"

"I told you, Demoness." Rhea sighed. "I will revive Mother!"

"tsk, tsk, tsk." Demoness laughed. "You already killed that Sitri woman, what's next, the professor? No wonder Byleth doesn't trust you!"

"halt, don't move!" Metodey begins. "If you move your lives will be forfeit!"

"My, My." Demoness says in a sarcastic tone. "Humans are so rude... Guess I'll have to show them some manners, for mother."

"We must stop those who raid the Holy tomb along with The Ashen Demon, both of their hearts are too wicked to be allowed to beat!"

**(Summery of the battle)**

The Ashen Demon attacked the Flame empire, they were injured but that didn't her, she _killed_ them. they were slaughtered.

"I'm going to end you... For the professor!" The Ashen Demon disguised her personality as Byleth's.

"N-No, Dimitri. It's me!" The Ashen Demon begins in Byleth's voice. "No, don't hurt me!"

_(Slash!)_

"Your foul tricks will not work on me, demon!" He yells.

"G-Gah..." The ashen demon grunts. "Y-You saw right through me..." She transforms into a dragon and flies off. Edelgard and Hubert have escaped while the Ashen Demon fled, leaving the crest stones on the floor.

"The war has begun." Rhea begins. "Not just against the empire, but against... _HER!"_

**(End of chapter 2)**


	3. Slaughter at Garreg March

**Summary for the Chapter:**

> During the battle of Garreg Mach, The Ashen Demon appears, slaughtering Empire forces and possible Church knights sending both armies into near depletion.

**Notes for the Chapter:**

> Possible support chats with Jeralt?  
> (Yes.)

"It's been a whole moon since we last encountered the Ashen Demon.." Rhea sighed.

"What is the Ashen Demon, Lady Rhea?" Cyril asked.

"The Ashen Demon is a... an entity that took control of our professor when Jeralt was almost killed." Rhea sighed.

"According to legend.." Dorothea begins. "It can destroy the planet, and it intends to do so."

"GAAAHHHHHHHHH!" Bernadetta begins. "What are it's targets?"

"For now?" Rhea asked. "The Ashen Demon is targeting the empire and it's possible generals. So being in their army is a death sentence... for now."

"This is giving me difficult... difficulty..." Petra sighed. "The dragon is a demon, is it not?"

"In that you are right, Petra." Ashe begins. "It's a dragon we have to get rid of to save our professor!"

**(Support conversation between Jeralt and Flayn: Rank:C)**

"Mister Jeralt?" Flayn asked.

"What is it, Flayn?" Jeralt asked.

"Are you still thinking about, her?" Flayn asked.

"Yeah... I am." Jeralt sighed quietly while sipping an alcoholic drink.

"Don't worry." Flayn smiled. "We'll find the Professor!"

"Say..." Jeralt begins. "Did your father take care of you or Seteth as kids?"

"Yes he did." Flayn says not wanting to draw attention to herself. "Why?"

"That kid..." Jeralt sighed. "That kid often worries me."

"How so?" Flayn asked.

"Just a worrying father, you know." Jeralt chuckled.

"Well. I have faith we will find her." Flayn smiled.

**(End of support conversation, battle of Garreg Mach.)**

"The empire is already here!" Dimitri says. "We better repel them." A sharp echoing roar pierces the quiet air.

"GWAAAAAAAAAAAAAAAAAAAAAAAAOOOOOOOOOOOOOOOOOOOOOHHHHHHHHHH!" The dragon roars.

"She's here, again.." Rhea begins. "Defeat the empire, _AND_ the Ashen Demon."

"Right." the blue lions say. The entire battle was tough for The empire, the two generals holding the strongholds provide the church reinforcements were killed. Hubert and The Death Knight were slain, sending fear into anyone who dared to oppose the Ashen Demon.

"Alright you beast, give me back my kid!" Jeralt yelled.

"GAWWWWWWWWWWWWWWOOOOOOOOOOOOOOOOOHHHHHHHHHHHHHHHHHH!" The dragon roared once again. It's wings spread out as it flew into the sky.

"Is that... TEACH?!" Claude asked.

"Gwaoh." The dragon replied as it flew off.

"She's gone.." Jeralt sighed. "That thing is gone with my daughter."

"We'll find her, Captain." Dimitri begins. "I am sure of it."

**(End of chapter 3)**

Idk if I should add more support conversations with Jeralt.


	4. Five years...

**Summary for the Chapter:**

> Five years have paced since the Ashen Demon was last fought... Five years with out a Professor and a daughterless mercenary is bent on getting the professor back.

Five years....

Five years have passed since the demon showed up.

Dimitri had woken up from another nightmare he had, he got up and went over to his journal and begins to write. 

" _Journal enter number 59:_

 _It has been 5 years since I last see her... Since I last saw the professor, Empire forces have been greatly slaughtered, Alliance and Kingdom are trying desperately to avoid being spotted by that thing. The fatalities are those loyal to the empire, Ferdinand is safe because he switched by targeting a beast in his army, Caspar and Lindhart weren't so lucky, being loyal to the empire is a death sentence now and most soldiers flee out of fear, all but a few who remain loyal... How long this mission takes, I wish to find and free the professor of being controlled by the beast."_ Dimitri quickly stopped writing.. He closed his journal and put it away.

"So?" Dimitri asked as he walked into a conference room. "Who will be our new professor?"

"Me." Jeralt grunts.

"Captain Jeralt?!" Dimitri asked. "You'll be our professor?"

"Something wrong with that?" Jeralt asked. "My kid's out there being controlled by a demon and your questioning me?"

"No." Dimitri begins.

"Look, I don't know what Byleth teaches you, but I'll try my best to keep up." Jeralt sighed.

A few moments had passed, The blue lions had been taught well despite Jeralt only teaching once.

**(With Byleth/Ashen Demon)**

"G-Gah! Huh?!" A voice asked as water was thrown on a woman.

"Nice to see your awake Monica... I mean, Kronya!" Byleth snickered.

"What do you want?!" Kronya angrily grumbled.

"Remember when you tried to kill my father?" Byleth snickered.

"I would've if that dragon didn't get in my way!" Kronya grunts.

"Aww! Scared of my true form?" Byleth mocked. "Your going to stay here for a long time... Don't think about getting out, the doorway and metal will kill you instantly..."

"They'll find you, dragon.. I'll make sure they do!" Kronya vowed.

"All your soldiers and allies have been slaughtered. Don't think you'll have anyone to save you." Byleth sighed.

**(End of chapter 4)**


End file.
